Solenoid starter motors and inertia starter motors are commonly used to start internal combustion engines.
Solenoid starter motors have a solenoid which moves the drive pinion between a disengaged position and an engaged position. These type of starter motors are also known as positive displacement starters as the solenoid ensures positive movement of the pinion into engagement with the ring gear of the engine.
A traditional inertia starter has no solenoid. Instead, the drive pinion is moved by inertia at the time the starter motor is turned on. The drive pinion has an output pinion for engaging the ring gear of the internal combustion engine, and a driver which is mounted on a drive shaft driven by the motor. The driver engages with a helical spline formed on the drive shaft so as to move axially along the drive shaft when the driver rotates about the drive shaft. When the motor starts, the inertia of the drive pinion initially prevents the driver from rotating with the drive shaft and hence the drive pinion is moved axially along the drive shaft and into engagement with the ring gear at which time further axial movement is restricted and the drive pinion rotates with the drive shaft. A one way clutch, also known as an overrunning clutch, may be provided to transmit the torque from the driver to the output pinion and to disengage the driver from the output pinion when the output pinion rotates faster than the driver.
Compared with solenoid starters, inertia starters apply a greater shock load to teeth of the pinion and the ring gear when the output pinion engages with the ring gear, which causes wear of the pinion and the ring gear, sometimes even causing the pinion to become jammed with the ring gear if the engagement between the pinion and the ring gear is not well matched. It is desired to solve the above problem.